Retractable drill bit



May 2, 1961 J. CAMP ET AL RETRACTABLE DRILL BIT Filed July 30, 1956 25 79|17 7740 35 42 A40 filo 4| n 7 I00 I13 llz FIG. HA)

2 Sheets-Sheet 1 FIG. I(B) John M. Comp Jackson M. Kellner By w-Attorney Inventors May 2, 1961 J. M. CAMP ET AL RETRACTABLE DRILL BITFiled July 30, 1956 John M. Comp Jackson M. Kellner By U119. Attorney 2Sheets-Sheet 2 Inventors RETRACTABLE DRILL BIT John M. Camp and JacksonM. Kellner, Tulsa, Okla., assignors, by mesne assignments, to JerseyProduction Research Company Filed July 30, 1956, Ser. No. 600,910

4 Claims. (Cl. 175259) The present invention concerns an improvedretractable drill for use in well drilling operations,' Moreparticularly, the invention concerns drilling apparatus including aretractable drill bit which is more rugged and dependable thanretractable bits that have been employed or suggested to date.

noted, is related to aretractable drill which is described and set forthin United States Patent application Serial No. 268,891, filed January29, 1952 in the name of John M. Camp. This application has matured intoPatentNo.

The apparatus of the invention includes a tubular drive sub which isattachable to the lower end of a string of well pipe. A tubular mandrelcarrying a plurality of suspended cutter elements is adapted to fitwithin the drive sub and is lowered within the sub to a point near thebottom of a bore hole. Latching devices or equivalent means are slidablymounted in slides on the mandrel and are alternately engageable withrecesses in the mandrel and in the drive sub. The slides supportelongated straps or equivalent members which in turn extend below thedrive sub and support individual cutter elements of the drill bit. 7

As the mandrel'is originally assembled and lowered within a bore hole,the latching devices engage recesses in the mandrel in a manner suchthat the slides support the drill bit cutter elements in a verticallyspaced, nested relationship- Then, as the mandrel enters and passesthrough the drive sub, the latching devices disengage from the mandrel,slide along the mandrel, and engage recesses within the sub.Simultaneously, the cutter elements protrude below the drive sub andassemble with one another in a manner to define an integral multi-cutterdrill bit. Once the latching devices engage and lock V within the drivesub, the center mandrel is free to move vertically downward anadditional distance suflicient to bear against innercontact shoulders ofthe cutter support members and thereby force the cutter elements intoticular orientation relative to the sub and therefore readily engage thesub without requiring pre-orientation.

An expansible sleeve packer of a type capable of very substantiallongitudinal compressive movement is provided .9 1 the mandrel and isactuated subsequent to assembly U ied St e PawO? 2,982,366 Patented May2, 1961 of the bit cutter elements to provide a fluid-tight seal in theannulus between the mandrel and the sub. Releasable interengaging meansare provided at the upper end of the mandrel for positively engaging thesub when the bit cutters have been assembled and the packer has beenset.

I Having briefly outlined the major structural components and featuresof the present apparatus, attention is now directed to the drawing for amore complete and clearer understanding of the invention. The drawingillustrates an apparatus constituting a preferred embodiment of theinvention which'is contemplated to be the best mode for practicing theinvention.

Figure 1 illustrates the apparatus of the invention in verticalcross-section, as the apparatus appears with its cutterelements in aretracted position for lowering within a bore hole. Figure 1(a)illustrates a lower portion of the apparatus and Figure 1(b) an upperportion.

Figure 2 illustrates the apparatus of Figure 1, again in cross-section,as the apparatus appears with the bit cutter elements expanded intodrilling position.

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Figure 3 is a section-view taken along the line IIIIII of Figure 2.

Figure 4 is a section-view taken along the line IV-IV of Figure 2. I

Figure 5 is a section-view taken of Figure 2.

Figure 6 is a partially sectioned viewv of a tool for expanding orretracting the apparatus of Figures l-5.

Referring to the figures, drive or drill sub 1 is an elongated tubularmember threaded at its upper end to engage drill pipe 2. The actualjunction of the sub with the drill pipe'may be a threaded connection asparticularly shown in Figure 1(b), or it maybe a welded joint, a boltedsection or other equivalent device. The drill sub preferably has aninternal diameter substantially equal to that of the drill pipe, and itsouter diameter may be somewhat larger than the drill pipe in order toprovide the sub with additional strength and ruggedness. The sub, itwill be recognized, may be considered as a particular type of drillcollar modified in the manner shown to meet the requirements of theinvention.

Near the upper end and interiorly of drill sub 1 is a circumferentialgroove 4, which possesses a downwardly facing shoulder 5. The lowerportion of the groove 6 is preferably tapered or inclined as illustratedfor reasons that will be apparent later in this description.

A second peripheral groove 7 is provided in a drill sub 1 at a pointintermediate its ends. This groove is provided with a lower upwardfacing shoulder 8 and an upper downward facing tapered shoulder 9 asillustrated. The lower end of drill sub 1 terminates in an inwardlytapered and downward facing shoulder 11, the angle of taper beingselected in a manner to be considered later in this description. 4

along the line V-Y Spaced slightly above shoulder 11 is a third groove 34 which extends around the inner periphery of drill sub 1. The upper andlower ends of this groove are preferably tapered as shown, the lowertaper or shoulder 12 defining a surface whose purpose will be clearlater in this description.

Disposed around the entire periphery of groove 3 are a plurality oflongitudinally disposed and radially spaced splines 18. As will beapparent later these splines coact with mating splines on each one ofthe cutter elements to effect a positive drive relationship between thesub and the, cutter elements. The upper terminal ends of each. splineare preferably tapered and rounded so that the splines on the cutterelements may freely engage the splines on the sub.

Thus, drill sub 1 is essentially an elongated cylindrical 3 nallydisposed circumferential grooves and shoulders, the purpose of which isto coordinate and coact with various other parts of the apparatus to beconsidered next.

Fitting Within drill sub 1 is tubular mandrel 13 which carries cutterelements 100, packer assembly 14, lower latches 15, and upper latches16. A central passageway 17 extends vertically throughout the mandreland provides means for transmitting drilling mud or other fluids fromthe interior of the drill string to the cutter ele ments of the bit. Thelower end of this passageway preferably terminates in the form of a jetfor better directing the drilling mud or other fluid at high velocityagainst the bit.

The outer surface of the lower end of the mandrel 13 is preferablytapered somewhat to resemble a frustoconical wedge. This structuralfeature enables the mandrel to apply a wedging action against the cutterelements 100 when the cutter elements are expanded into a drillingposition and engaged with the lower end of the drive sub. The cutters ofthe cutter elements, as illustrated, are preferably cone-type cutters. I

Disposed above the lower tapered portion of the mandrel and extendingupwardly along the length of the sub, are elongated grooves or slots 20which provide vertical runways for movement of slides 21 and 22. Theseelongated grooves do not extend the entire length of mandrel 13 butinstead terminate below the packer assembly 14 at the shoulders 24.

The upper end of each slide is recessed internally with a cavity 23.Disposed within each cavity a latching dog 15, each dog being normallyurged radially outward by means of springs or other equivalent resilientdevices not shown. The dogs, it will be noted, are provided withshoulders at each vertical end which engage retaining shoulders on theslides, thereby retaining the dogs positively within the slides. Thedogs themselves are preferably tapered on their outer and upper ends soas to enable them to disengage readily from sub 1, when suchdisengagement is desired.

Secured to the lower ends of the slides are elongated straps orequivalent supporting members 25 which are attached or secured to'shanks 37 of cutter elements 100.

Each slide 21 and its attached strap lies within a elongated groove orslot 20 formed within the wall surface of mandrel 13. Thus, each slideand its attached strap is able to move in a vertical orlongi'tudinalslidable manner relative to the mandrel.

Vertically spaced recesses and 31 are positioned along the mandrel 13,each recess being in alignment with one of the slots 20. It is thepurpose of these recesses to contain the lower latching dogs 15, as the'tool is lowered in the hole, to prevent any movement of the cutters 10,the strap 25, and the slides 21 with relation to the mandrel 13 beforeall of these parts reach the proper position within the drive sub. Itwill be apparent that vertical spacing of the recesses 30 and 31 isrequired in the illustrated apparatus in order that the verticallyspaced cutters in a retracted position may be placed in the samehorizontal plane in their expanded or drilling position.

At this point it will be noted that the apparatus in the drawing isshown to possess two cutter elements. An apparatus with two cutters hasbeen chosen to illustrate and describe the invention, since descriptionof such an apparatus is relatively straight forward and readilyunderstood. It should be pointed out, however, that an apparatusemploying three cones is actually preferred for the purposes of theinvention. In the latter instance the cutters are space 120 apart ratherthan the 180 shown in the present drawing.

It should also be noted at this point that it is essential for thecutters and their associated straps and slides to be distributed in anequally spaced manner around the periphery of the center mandrel.Furthermore, the number of splines 18 in the lower portion of the drillsub 1 should be evenly divisible by the number of cutter elements in thebit portion of the apparatus. For example, 60 splines would be suitablefor use with bits containing two to six cutters. It has been ascertainedthat engagement of the splines 18 in the drill sub and the matchingsplines associated with each cutter element is readily and cleanly madewhen this Condition is observed. If this condition is not met, thecutter elements will have a different angular spacing in an expandedcondition than they possess in a retracted condition; and the mandrelwill be generally unable to force the cutter elements into complete andsmooth engagement with the drill sub. In addition, it is necessary thateven spacing of the cutter elements be observed in order to take fulladvantage of the space available at the bottom of a borehole. It followsthat the number of teeth or splines on the drill sub must be an evenmultiple of the number of cutters; otherwise, such even spacing isimpossible.

Each cutter element 100 is attached to its respective strap 25 by meansof a pivot pin 35. The pins provide the cutters with a degree ofmovement necessary for them to be expanded and retracted as desired.

The shanks 37 are provided with an anglar configuration to coordinatethese members with the mandrel and the drill sub. Specifically, eachshank is provided with an inner shoulder 40 which is tapered to coincidewith the lower tapered end of the mandrel. A lower outer shoulder 41 isprovided to coincide with the shoulder 11 at the bottom end of sub 1;and an upper outer shoulder 42 is provided to coincide with and bearagainst the lower taper or shoulder 12 of the sub.

The lower outer shoulder 41 of each shank should form an angle with thevertical of between about 35 and 45, since it has been found that anglesin this range provide a unique advantageous distribution of thrust andspace for the expansion and retraction of the cutter elements. Mostconventional cone-type bits have pin angles of about 39; and it has beenobserved that when using such cutters, the angle with the vertical ofthe shoulders 41 should likewise be about 39 for best overall results.

Insofar as the angular disposition of the upper outer shoulders 42 areconcerned, it is preferred that these shoulders form an angle of atleast about 30 from the vertical and preferably at least about 45. Anangle of should not be exceeded.

A packing element 14 is mounted on mandrel 13 at a point verticallyabove shoulder 24. As illustrated, the packing element should be asleeve-type element which resembles a bellows in structure and which iscapable of radial expansion in response -to longitudinal compression. Itis necessary and desirable that the packer element be of a character toset under relatively low loads and that it further be characterized bysubstantial longitudinal compression.

The packer element should be constructed of an elastic, deformablematerial-preferably natural or synthetic rubber-and it should be pleatedas indicated to resemble a bellows. It has been found that verysubstantial longitudinal movement is attainable with the bellowsconstruction and such movement is necessary in order that the latchingdogs may properly coordinate and engage the sub 1 and the mandrel 13.Conventional rubber sleeve packers have been tried in this application,but they have been found to require setting loads which are impracticaland undesirable in the practice of this invention. On the other hand,the bellowsor accordionshaped packer illustrated in the drawing has beenfound to combine all of the features that are-necessary to insure properand dependable operation of the apparatus.

Referring more particularly to packer assembly 14, it will be observedthat lower pleat 50 actually contacts and provides a sealing surfaceagainst the inner wall of sub 1, whereas the upper pleat 51 does notcontact the sub completely around its periphery. Thus, pleat 51 maysausages ly a slot 52 may be cut through pleat 51. Furthermore, it willbe observed that a longitudinal groove or passageway 53 is providedalong the length of mandrel 13, the purpose of this groove or slot beingto vent the inner cavity portions 54 and 55 of the bellows to theinterior passageway of the mandrel. It is then impossible for liquid tobe entrapped in any of the cavities that are formed between the pleatsof the packer assembly 14 when this assembly is expanded into contactwith the sub. Any liquid so entrapped has been found to impair theability of the packer to compress under light loading,

and the venting passageways are therefore vital to the successfuloperation of the packer.

Packer assembly 14 is held against the, outer wall surface of mandrel13- by virtue of upper retainingring 60 and lower retaining ring 61.Lower ring 61 is secured directly to mandrel 13, while upper ring 60 isattached to sleeve 62 which is vertically moveable relative to themandrel. Thus, a vertical force or thrust downward against sleeve 62drives this member plus upper retaining ring 60 vertically downwardrelative to the mandrel and thereby compresses the pleats Stland 51.Pleat 50 seals against sub 1, and both pleats-Le. pleats 50; and51contract longitudinally a distance sufiicient to enable the sets oflatching dogs to engage, the proper grooves at the proper instant.

assembly is suspended from the spearhead. The dogs 16 are maintained ina retracted condition by contact with the inner surface of the drillpipe; and, since packing assembly 14 is under no compressive loading, italso is in a retracted position. Cone cutters 10 of the bit are inaretracted, vertically nested condition, the slides 15 being locked orin engagement with the recesses 30 and 31 in mandrel 13.

Upon being lowered within drill sub 1, the mandrel and its associatedparts coact with the sub in the follow? ing sequence. First, the lowerone of the two latching dogs 15 reaches groove 7 and pops out into thegroove from recess 31. Since d0g'15 is clear of mandrel 13 when itengages groove 7, mandrel 13 is free to move vertically downwardrelative to the lower dog.

Simultaneously with the entry of the lower dog '15 into groove 7, lowercutter l0 expands into a drilling position immediately below the lowerend of the drive ,sub. In other words, the lower outer shoulder 41 andthe upper outer shoulder 42 of the shank attached to the lower cutterengage shoulder 11 and shoulder 12, respectively, of the drive sub.Similarly, splines 91 of the cutter shanks e'ngage the matching splines18 of the sub.

At this point is should be noted that sleeve 62 extends up beyondmandrel 13 and is provided with two ports 70 through which upper dogs 16are able to pivot.

' Both dogs are pivoted about pivot pins 72 which in turn are mounted insleeve 62. The upper ends of dogs 16 are provided with outer upwardfacing shoulders 71 adapted to engage shoulder 5 on drill sub 1; andthey are also provided with inner downward facing shoulders 73 which areadapted to engage the spearhead 74 of a tool for raising or lowering themandrel and its associated parts. The dogs are normally urged outwardlyas by means of a suitable spring or other resilient element notillustrated.

The upper end of each upper dog 16 is provided with a tapered section75. The purpose of this tapered section is to enable a suitable tool tourge the dogs radially .inward, when it is desired to retract the drilland raise it ,from within the drive sub. An example of a suitable toolis shown in Figure 6 and includes sinker'bar 80, upper spearhead 81,stem 82, spring 83', retracting sleeve 84, ,lower spearhead 74 and pin85. Sleeve84 is slideably moveable on stem 82 and is normally urgeddownward 'from sinker bar 80 by means of spring 83. The tool isillustrated in Figure 6 with the spring in its expanded position; and itis in this condition that the spring is employed to retract the drillassembly. The pin 85 is not inserted in the tool in this instance.Lifting of the drill by the tool is actually accomplished when the innershoulders 88 on the dogs 16 engage the shoulders 89 near the top of themandrel.

When the tool in Figure 6 is to be used to lower the :drill into a borehole, spring 83 is compressed, and pin 7 85 is inserted inthe holes 86and 87 to hold the spring in its compressed position. Sleeve 84 isprovided with a conical recess at its lower end to enable the sleeve toretract dogs 16 by bearing down upon shoulders 75. .Upper spearhead 81is attachable to a wire line or equivalent means for raising andlowering the retracting tool.

Having described the various structural components of the apparatus inthe drawing, attention is now directed For this purpose it willbeassumed Referring to Figure 1, the apparatus is there illustrated inthe condition required to enable it to be lowered within a bore hole.The spearhead 74 of the lowering tool illustrated in Figure 6 is inengagement with the shoulders 73 of the retractable upper'dogs 16, andthe entire-bit Subsequent to engagement of the lower of the two cutterelements 100 with drive sub '1, mandrel 13 continues vertically downwardwith its remaining lower dog and cutter element-Le. the upper of thedogs 15 and the upper of the cutter elements 100. When the remaining dogreaches groove 7, itlike the first dog-pops into the groove anddisengages itself from the mandrel. Simultaneously, its cutter expandsinto a drilling position radially opposite the first cutter. Then,mandrel 13, being free of both locking dogs, slides down relative toboth cutters until its lower conical wedging surface bears against theinner shoulders 40 of shanks 37. This action on the part of the mandrelserves to wedge the shank portions and their attached-cutters firmly indrilling position. The spline segments 90 on each shank are now inengagement with the spline 18 of the drive sub.

At this point-it is well to note that it will be generally a necessaryto employ sinker bars or other weighted devices for applying a load onthe mandrel which is sufficient to wedge the cutters and theirattachedshanks into a drilling position. As illustrated in Figure 6,such sinker bars or other weights may be incorporated directly ascomponents of the tool which is used to raise and lower the drill.

Once the cutters have been wedged into drilling position at the bottomof drill sub 1, expansion of the packer assembly 14 is the next step inthe operating sequence. Briefly, the aforementioned sinker bar or otherweight exerts a downward thrust through spearhead 74 and the upper endof sleeve 62 which is sufiicient to drive the sleeve vertically downwardagainst retaining ring 60 and pression of the bellows results. Thiscompression in turn causes the individual pleats 50- and 51 to contractvertically and to expand radially. Any liquid entrapped within the innerperipheral cavities 54 and 55 is vented through slot 53 into theinterior passageway within the drive sub and the well pipe above thesub. Similarly, any liquid entrapped in the outer peripheral cavity 81defined by the two pleats is free to vent upwardly in the annular spacebetween the upper retaining ring 60 and the sleeve 62 into the drive subpassageway.

Longitudinal contraction and radial expansion of the packer results inpleat 50 forming a peripheral seal between the mandrel portion of theoverall assembly and the inner wall surface of the drive sub. The degreeof compression and the degree of sealing may be readily means ofthesinker bar or other weight.

Concurrent y with the setting of the packer, upper dogs 16 are forcedoutwardly until they come laterally opposite the upper groove 4 in drivesub 1. Since the spearhead 74 is now bearing directly against sleeve 62it follows that dogs 16 are free to expand and ride along the innersurface of sub 1 until they reach groove 4. At this time they expandfurther and enter groove 4.

The drill is now in condition for drilling, and spearhead 74 may berais-d vertically from the apparatus and removed from the bore hole.Actual drilling is obtained by lowering the drive sub and the attachedwell pipe above the sub until the cutters reach the bottom of the borehole. Rotation of the bit, the drive sub and the well pipe is obtainedby use of conventional surface rotary equipment; and loading of the bitis likewise controlled by means of conventional surface apparatus.Downward thrusts on the well pipe are transmitted through dogs 16 tosleeve 62 and thence through the bellows packer and the mandrel tomaintain the cutter shanks 37 in a locked relationship in the drive sub.Simultaneously, downward thrusts on the well pipe are transmittedthrough the shoulders 11 on the drive sub to shoulder 41 on the cuttershanks to apply drilling loads to the cutters.

7 When a drilling operation has been interrupted and it is desired toremove the drill from a bore hole, the following sequence of operationsis employed. First, the well pipe and drive sub 1 are removed or liftedfrom the bottom of the hole, and rotation of the equipment is ceased.The tool illustrated in Figure 6 with pin 85 removed is lowered throughthe well pipe. When the spearhead 74 of the tool reaches the upperlatches 16, the inner conical surface 90 of the tool forces the latchesradially inward from the groove 4 so that they disengage .from the sub 1and in turn engage the spearhead. An

upward pull on the tool then causes upward movement of sleeve 62 with aresultant longitudinal expansion and radial contraction of the packer.

Upward pull of the tool also lifts the mandrel 13 with .the result thatcutter elements 100 are retract d from their drilling position andlifted within the drive sub in a sequence which is substantially thereverse of the sequence by which they. were expanded into the drillingposition. Thus, the right-hand cutter in Figure 2 is the first of thecutters to be retracted and withdrawn, and .the left hand cutter thenfollows.

Simultaneously with the retraction of the cutters, up-

ward pull of the mandrel 13 causes the slides 21 and 22 to besequentially engaged and lifted relative to the drive sub., As theslides move upward in their slots 21, they force dogs 15 to be retractedfrom the groove 7 and to enter the recesses 31 and 30. At this point thedrill is in a fully retracted position and may be lifted to the surfaceof the earth.

It will be apparent that the drills of this invention are preferablyoperated by means of wire-line apparatus. It

"will further be apparent that the apparatus may be constructed from theusual materials such as steel, rubber and the like that areconventionally used in drilling equipment. Furthermore, it will berecognized that conventional drilling techniques such as the use ofdrilling mud cutter elements suspended therefrom in a vertically spacedrelation when the drill is in a retracted condition, the cutter elementsbeing assembled immediately below the drive sub and wedged'between themandrel and the sub when in a drilling. position, the improvement whichcomprises a plurality of longitudinally disposed splines equally spacedand extending around the lower inner periphery of the drive sub, atleast one longitudinal spline on an exterior portion of each cutterelement, the splines on the drive sub being sufiic'i'ent in number andan even multiple of the number of cutter elements so as to enable thecutter elements to be assembled in a drilling position withoutpro-orientation, a longitudinally compressible, radially eXpansible,laterally pleated sleeve packer around and supported at its lower endfrom the outer wall surface of the mandrel; means to vent the cavitiesdefined by the pleats of the packer, said packer upon longitudinalcompression within the drive su'b being adapted to seal the annulusbetween the drive sub and the mandrel.

' 2. In aretractable drill of the type described including a tubulardrive sub attachable to the lower end of a string of well pipe, and atubular mandrel adapted to move longitudinally within the well pipe andthe sub, the mandrel carrying a plurality of cutter elements, a packerassembly and retractable latching means when the drill is in a retractedcondition, the mandrel and its associated parts being cooperable withthe drill sub to assemble the cutter elements below the drive sub and tolook the cutter elements in their assembled condition, the improvementwhich comprises a plurality of longitudinally disposed, equally spacedsplines extending around the inner periphery of the sub and spaced fromthe lower end thereof, at least one spline on the exterior upper surfaceof each cutter element adapted to engage the splines on the sub, thenumber of splines on said sub being sufiicient in number and an evenmultiple of the number of cutter elements so as to enable the cutterelements to be assembled in a drilling position without pre-orientation,a lower exterior portion of each cutter element defining a tap"redsurface forming an angle of about 35 to 45 with the vertical when thecutter element is in an expanded position, the lower end of said drivesub having a downward-facing tapered surface adapted to engage with thetapered surfaces of the cutter elements when in their expanded position,said packer assembly comprising a longitudinally compressible, radiallyexpansible, laterally pleated sleeve packer and including means to ventthe cavities defined by the pleats of the packer.

3. In a retractable drill of the type described including a tubulardrive sub and a cutter element-carrying tubular mandrel longitudinallymovable Within the drive sub, the cutter elements in a retractedcondition being suspended in a vertical array from the mandrel and in adrilling condition being wedged between the lower ends of the mandreland the sub, and an expansible packer assembly on the mandrel operableto elfect an annular seal between the mandrel and the sub, theimprovement which comprises longitudinally disposed splines recessedwithin and equally spaced around the interior surface of the drive subat a point spaced from the lower end of the sub, a downward-facingperipheral shoulder inclined at an angle of about 35 to 45 with thevertical on the internal surface of the sub below the splines, eachcutter element including an upwardfacing external shoulder adapted toseat against the peripheral shoulder of the sub, longitudinally disposedsplines on each cutter element above the shoulder portions thereof toengage the splines on the sub, said packer assembly comprising alaterally pleated, longitudinally compressible sleeve packer, and meansto vent the cavities defined by the pleats thereof, the splines on saidsub being suflicient in number and an even multiple of the number ofcutter elements so as to enable the cutter elements to be assembledwithin their drilling position without pre-orientation.

4; In a retractable drill of the type described includ- ,ing. a tubulardrive sub attachable at its upper end to the lower end of a string ofwell pipe and a tubular mandrel longitudinally movable within the wellpipe and the drive sub, the mandrel carrying a plurality of cutterelements suspended therefrom in a vertically spaced relation when thedrill is in a retracted condition, the cutter elements being assembledimmediately below the drive sub and wedged between the mandrel and thesub when in a drilling position, the improvement which comprises aplurality of longitudinally disposed splines equally spaced andextending around the lower inner periphery vof the drive sub, at leastone longitudinal spline on an exterior portion of each cutter element,

the splines on the drive sub being sufiicient in number and an evenmultiple of the number of cutterelements so as to enablethe cutterelements togbe'assembled, in a drilling position withoutpre-orientation, a longitudinally compressible, radially expansiblesleeve packer surrounding and supported at its lower end by'the outerwall surface of the mandrel, said packer upon longitu- 10 dinalcompression within the drive sub being adapted to seal the annulusbetween the drive sub and the mandrel.

References Cited in the file of this patent UNITED STATES PATENTS CampSept. 25, 1956

